a. Field of the Invention
This invention relates to an electrophotographic method and an apparatus therefor. More particularly, it is concerned with an image forming method and an apparatus which make it possible to selectively reproduce only the required region of an image original.
b. Description of the Prior Arts
Heretofore, when a required region of an image original is selected for reproduction (or copying), there have been adopted various methods such that: (1) a part of the image original is cut out; (2) the unnecessary portion of the image original is folded so as not to be exposed to light; (3) the unnecessary portion of the image original is covered with a masking member such as white paper, etc., and various other methods. Of these, the methods (1) and (2) are inefficient, because the work is done manually, and moreover they are impossibly applicable to those image original which is books or other hard materials. On the other hand, the method (3) is difficult to set the masking position on the image original; in particular, when the image original is placed on a image original placing table, the marking condition of the image original cannot be verified by an operator, which makes it difficult to set the masking position.
In view of the above-described inconveniences, there have so far been contemplated the following methods for obtaining only the required portion of the image original from the electrophotographic reproduction apparatus.
(i) In the electric charging step, the unnecessary image region on the photosensitive body is prevented from being charged.
(ii) In the developing step, the unnecessary image region on the photosensitive body is prevented from being developed.
(iii) In the image transfer step, the unnecessary image region on the photosensitive body is prevented from being transferred.
Since the abovementioned three methods (i), (ii), and (iii) do not visualize the unnecessary image region, it is necessary to partially interrupt the charging, developing or image-transferring operation. For this purpose, it is required to interpose a covering or masking member between the photosensitive body and each of the above-mentioned processing means, or to effect complicated electrical control operations. In addition, the above-mentioned three methods tend to lack in accuracy their operation. For example, in the method (i), a boundary between the electrically charged section and the non-charged section of the photosensitive body becomes ambiguous owing to the covering member interposed between the corona discharge electrode and the photosensitive body with the consequent inability to form an image, in which such desired required image region is clearly distinguished by a very sharp and clear boundary line. In the methods (ii) and (iii), toner particles adhered onto the covering member are liable to contaminate the image transfer material and the photosensitive body.